The present invention relates to improving the density of cast parts. In particular the invention relates to improving the density of cast lead parts and most particularly to improving the density of cast lead parts which are used in the construction of lead-acid storage batteries.
A variety of lead parts, such as battery posts, lugs, etc., are used in the construction of lead-acid storage batteries and are generally referred to as small parts. These battery parts are subject to the corrosive effects of the battery acid and acid gases as well as the stresses, shocks, vibrations and strains associated with battery manufacturing and usage. Storage batteries used in vehicles, such as trucks, cars, and the like, are particularly subject to rough abusive treatment. The failure of a single cast part can render the entire battery useless.
One technique for casting lead battery parts is to employ an open mold having mold cavities defined therein and configured to produce the respective parts. The mold is passed beneath a ladle containing molten lead to position each of the cavities thereunder. As a cavity becomes positioned beneath the ladle, the molten lead pours into the cavity via a sprue in the bottom of the ladle. Another technique is to use a stationary mold and a movable ladle.
Although the previously described casting technique may produce satisfactory parts, often the air which is contained in the mold cavity is trapped within the part as cast. This trapped air forms imperfections in the cast parts which can result in reject parts and/or weaken the parts and causes them to fail during usage.